Rep. Mike Coffman has been called the winner of a fifth term. (Bill Clark/CQ Roll Call file photo)

Republican Rep. Mike Coffman has prevailed in Colorado’s 6th District, one of the closest-watched House races in the country, with The Associated Press projecting he will beat Democratic challenger Morgan Carroll.

Not all districts are created equal. They all count the same when adding for a majority, but victories in one type of district may portend a much better night for Democrats than in others. With just four days to go until Election Day, Democrats almost surely won’t gain the 30 seats needed for a House majority on Tuesday. But they will make some gains. Here’s where to watch for early clues as to just how big or small Democratic gains will be.

To achieve double-digit gains, Democrats must win the known battlegrounds. These are the districts that always were going to be competitive, and where presidential year turnout usually gives Democrats an advantage. At the very least, Democrats need to win the districts that President Barack Obama carried — places like Illinois’ 10th District, Nevada’s 4th and 3rd Districts, Maine’s 2nd District, Florida’s 26th District, (which is now even more Democratic), Iowa’s 1st District and New York’s 19th District. If they’re not able to win these seats, Democratic gains in the House will likely be very minimal.

The Democratic Congressional Campaign Committee made a $10,000 cable television buy Friday afternoon for an ad that pushes back on Colorado Rep. Mike Coffman's assertion that he'd stand up to Donald Trump if he's elected president.

Coffman on Thursday became the first vulnerable House Republican to release a video online in which he said he doesn't like Trump.

Democrats are focusing on more suburban districts, where they believe changing demographics are moving seats into the Democratic column, in their effort to regain the majority in the House. (Tom Williams/CQ Roll Call file photo)

As Democratic chances of taking back the House improve with the success of Donald Trump and Ted Cruz, party strategists are trying to figure out exactly how and where it’s going to happen. It’s not too difficult to see Democrats gaining 10, or even 20, seats in November, but gaining the 30 required for a majority is more difficult and will require Democrats winning a large swath of seats where Republicans are currently heavy favorites.

Winning the House majority is more than focusing on the presidential margin and allotting House seats to Democrats because of the strength of some GOP incumbents. For example, Democrats are not going to defeat Republican Rep. Frank A. LoBiondo this year, even though President Barack Obama won New Jersey’s 2nd with 54 percent, or win New Jersey’s 3rd (which Obama won with 52 percent), where wealthy GOP Rep. Tom MacArthur could easily outspend any challenger.